There are at present a number of different dental implants in use. Mostly the dental implants include a solid artificial tooth (implant) root portion which is placed into a custom bored hole in the jaw bone, and the outer portion directly coupled with a crown. A prosthetic coronal section is attached to the artificial root portion when healing and bone integration of the artificial root portion is complete, and a dental prosthetic appliance such as a crown, denture or bridge is attached to the coronal section.
When posts are to be anchored for a fixation of dental suprastructures, such as bridges or web-like stiffeners, implants are inserted or screwed into a pilot bore, which sometimes has been drilled into the jaw bone.
One of the dental implants is disclosed in the U.S. Pat. No. 4,863,383. The described implant includes a screw, which is formed with sharp-edged screw threads on a tapered shank. The shank is integral with a socket, on which the self-tapping screw threads are continued. In accordance with the invention the depth of the screw threads continuously decrease to zero in the direction from the tip of the shank to the outer end of the socket 4 so that the outside diameter of the rod-shaped implant remains constant from its top to the inner end of the screw threads. A zero depth of the screw threads is reached 2 to 3 mm below the butt joint. To facilitate the self-tapping operation, one or more indentations are formed in each convolution of the screw threads. For the same purpose the shank if formed in its tip portion with notches, each of which has a sharp edge which extends generally in the longitudinal direction of the shank and defines a surface that faces in the sense in which the implant is rotated as it is screwed into the bore. Those side faces of the screw threads which face the tip of the shank are at right angles to the axis of the shank and those side faces which face the socket include an obtuse angle with said axis. The post comprises a stem, which at its inner end carries male screw threads. The socket has a socket opening, which has a non-circular outer portion, which may be hexagonal as shown in the illustrated embodiment, and which is engageable by a mating socket key. The socket opening comprises at its inner end a blind circular bore, which is formed with female screw threads. The male screw threads of the stem of the post are screwed into the female screw threads. Those portions of the socket and of the post which abut at the joint have cylindrical outside peripheral surfaces which are equal in diameter and flush with each other. To permit the post to be secured in the socket, the stem of the post is formed with recesses for receiving adhesive paste or cement of the like, which will prevent a rotation of the post. For the reasons stated hereinbefore the female screw threads and the male screw threads of the stem may be left-handed. The socket has at its outer end a circular outside rim, which is adjoined by a threadless cylindrical outside peripheral surface having an axial width of 2 to 3 mm. The socket tapers from said cylindrical outside surface to the shank. The self-tapping screw threads terminate at said cylindrical outside surface.
This dental implant eliminate the necessity to drill a bore into the bone, but there is no universality of the outer portion for interchangeability between the currently available crowns and/or crown's systems. So, that once an implant has been mounted on one type of artificial root, any future replacements must use the same crown attachment system. Since the average lifetime of a crown is of the order of 7-10 years, at which time a patient may have moved or be seeing a different dentist, significant problems can arise when a crown replacement is needed. The dental practitioner must always have the same crown systems on hand, since patients may have been fitted with various different types of implants at different times, and will also need the appropriate set of tools for mounting the various systems. This problem is likely to become more acute as the number of individuals fitted with such implant systems increases.
Another problem with existing attachment systems is that of adjusting for undesirable placement angulation of the submerged artificial root. Since the prosthetic coronal section or post normally extends coaxially from the artificial root, and the prosthesis must be mounted on this post, undesirable angulation may make it difficult to align the prosthetic tooth or teeth with the natural tooth line. This is a particular problem with front teeth, since for cosmetic reasons it is desirable that a screw or the like securing a crown or artificial tooth to the post does not exit through a front face of the tooth. Some attempts for adjusting angulation are provided in various existing systems, for example providing the post or prosthetic coronal section with a bendable neck portion, but this results in a weakened area which is liable to break. In other systems fixed angled portions are provided on the post, but this allows one angular adjustment only and thus does not allow easy adjustment or a wide range of angulation adjustment.
Another problem with replacing front teeth with existing implant systems is that the post or prosthetic section securing the artificial tooth or teeth to the implant will often be visible between the base of the tooth and the gum, particularly as the gum recedes naturally with time. This results in an unattractive gap which can be seen when the wearer smiles.
One of the dental implant attachment system is shown in U.S. Pat. No. 5,015,186. According to this invention, a dental implant attachment system for mounting a dental prosthesis on an artificial root implant comprises a base member having a lower end sized to seat on the upper end of the root implant cylinder and an upper end having an outer diameter substantially equal to that of a tooth for mounting on the implant, and a prosthetic head having a lower end for mounting on the upper end of the base member and an upper end for securing to a dental prosthesis. A securing assembly is provided to secure the base member to the implant cylinder and the prosthetic head to the base member. The base members include members sized to seat on any existing artificial implant cylinder, and members having upper ends of diameter equivalent to a variety of average natural tooth sizes, for example in the range from 3.5 mm to 7.0 mm. The prosthetic heads have lower end cuff portions sized to seat on the upper end of each of the base members with no overlap, and each have an upwardly projecting post portion preferably of tapering conical shape. The prosthetic heads include post portions at angles between 0 and 30 degrees to the cuff portion, to allow for angulation adjustment. The prosthetic heads include a 0.5-2 mm wide butt joint which allows for a thickness of metal and ceramic to be placed between the post portion and the edge of the base portion. The securing devices such as screw fasteners is provided for securing the selected base member to the implant cylinder and for securing the selected prosthetic head to the base member. The upper end of the base member and lower end of each prosthetic head include interengageable indexing formations for securing the prosthetic head against rotation on the base member in any one of a series of fixed, indexed positions. The angled prosthetic heads can be rotated through 360 degrees relative to the base member to select the indexed position providing the best possible angulation before locking the head to the base member. In one arrangement the interengageable formations comprise corresponding male and female configurations each having flats around their outer diameter. The male and female configurations comprise hexagon or octagon nut and bore formations. With an octagonal locking formations, the prosthetic head is engaged in any one of eight possible different angular indexed orientations relative to the base member.
The interengageable formations will prevent rotation between any of the prosthetic heads and the base member to which they are attached, reducing the risk of loosening of the attachment structure as a result of dental forces, and also allow rotation of the angled heads into any one of a plurality of different possible fixed, indexed positions to adjust for the optimum orientation of the angled heads in the jaw. The fixed orientation of interengageable locking formation of the base member when mounted in the jaw establishes an indexing position for orientation of the finished prosthesis made in the laboratory. Thus the prosthesis can be precisely positioned on to the base member in the mouth. Also, the prosthetic head includes an annular member having a concave indent for seating a convex end element of the post portion. The post portion can be swiveled relative to the concave indent to adjust the angle of the prosthetic head post as desired. In order to mount any type of prosthesis on any artificial root implant cylinder, the base member having the appropriate lower and upper end dimensions is selected. This member is suitably mounted and secured to the implant cylinder. An impression head is then fastened to the base member, and impression is taken. The impression head is removed and may be replaced with a healing cap or with a temporary crown form. An analog of the base member is then fastened to the impression head and the analog and impression head are inserted into the impression. A cast is then made, into which the analog is set at the appropriate orientation. The impression head is removed, and the cast model of the patient's jaw with the embedded analog is used in a laboratory on a dental surveyor to orient an appropriate prosthetic head, either with a straight, angled or swiveling post section for increased adjustability. The selected prosthetic head is mounted on the base member analog at the optimum angular orientation. An appropriate wax pattern is crafted by those skilled in the art to exactly fit the prosthetic head. The prosthetic cast is then made from the wax pattern, and the parts are disassembled. The dentist can then reassemble the parts, mounting the prosthetic head on the base member in the patient's jaw and then cementing or otherwise attaching the prosthesis to the prosthetic head. The indexing locking formations between the prosthetic head and base member allows indexing between clinical and laboratory work and also allows for correction of undesired placement angulation of the submerged implant cylinder by choice of suitable angled prosthetic heads. They also make the attachment structure into a single fixed unit since the separate parts cannot rotate relative to one another once they are secured together.
This device is complex, has tall outer portion and does not provide the universality of the lower portion (root portion) for interchangeability between the currently available crowns and/or crown's systems.
Some other connecting device are known in the art, for example, the devices described in U.S. Pat. Nos. 4,746,293 and 4,756,689. Referring to the U.S. Pat. No. 4,746,293, the device includes the upper portion of a spacer, which is disposed on an anchorage unit implanted in jawbone tissue. The spacer is provided with a central, cylindrical spacer screw designed specifically for this purpose with an extended, exteriorly threaded pin. The spacer is provided with a collar consisting of two surfaces: an outer horizontal surface and an obliquely inclined surface located inside the surface. The connecting device in the form of an outer, sleeve-shaped patrix 6 is connected to the spacer. The outer circumferential surface of the patrix connects to the outer prosthesis portion by casting, and the patrix is so designed that it surrounds the central spacer screws. The base of the patrix connects to the collar-shaped portion of the spacer by the intermediary of a resilient member in the form of an O-ring of high-quality rubber. The spacer and the spacer screw are preferably made of titanium, while the patrix is suitably made of dental gold. The obliquely inclined surface of the collar-shaped portion of the spacer forms, together with an upper horizontal surface on a cuff of the spacer, two of the walls of an annular tunnel for the resilient member, namely the lower horizontal wall and the oblique lateral wall. The remaining walls of the annular tunnel viz. the medial, vertical wall and the upper horizontal wall are formed by the circumferential surface of the spacer screw, which in this case is of circular profile, and the planar, lower base surface of the patrix, respectively. The annular tunnel is formed by the above-mentioned surface is adapted to the resilient member in the form of an O-ring of rubber. In this case, the O-ring is dimensioned to permit a deflection of the order of magnitude of about 100-200 .mu.m. In eccentric or oblique loading, this corresponds to a maximum angular displacement of 1.degree.-2.degree.
The patrix surface is so disposed as to depress the O-ring and provide the contemplated elastic transmission of forces between the outer prosthesis portion and the spacer (the fixture). The play provided between the patrix surface and the spacer collar surface should exceed 200 mu.m in order to permit the planned elastic deflection of 100-200 mu.m. The elastic connection is anchored (locked) by an interiorly threaded special nut manufactured of, for example, gold. The nut is screwed onto the exteriorly threaded pin of the spacer screw such that its lower peripheral end surface meets a horizontal heel on the patrix. The nut is screwed on so far that light compression of the O-ring is attained. This light compression or pre-tensioning may be exactly determined in that the screw slot which is disposed in the top of the nut is turned so as to register with a groove in the upper patrix edge. By provision of further two such groove markings in the patrix edge to which the screw slot can be turned, both moderate and hard pre-tensioning of the connecting device may be mode, depending upon the deflection amplitude which is deemed to be most purposeful in each individual situation. The upper surface of the special nut may be covered with, for example, a gold washer once it has been locked by a droplet of acrylate. Acrylate is then applied over the gold washer in order to fill the aperture through which the nut was applied.
According to the mentioned U.S. Pat. No. 4,756,689, the device comprises the upper portion of a spacer which is disposed on a fixture (not shown) implanted in the jawbone tissue. The spacer is provided with a central, cylindrical spacer screw with a threaded bore for a locking screw. The spacer is provided with a collar which, in the extant systems, forms a substrate for the mounting cap (matrix) which, in turn, is united with that crown or bridge construction which is to be set in place. The locking screw is provided with a conical, downwardly tapering surface for fixedly locking the cap. Both the spacer and the locking screw. Also device comprises the cap-shaped matrix, for example of dental gold, titanium or plastic. Its base connects to the spacer in the same manner as does the cap in the extant system. The matrix is provided with an exterior thread arrangement (M4.times.0.5) for a ring nut. The matrix is further provided with an abutment or shelf adapted to the resilient member in the form of, for example, an O-ring of high-quality rubber for example EPDM (ethylene-propylene) rubber and, is dimensioned to permit a downward deflection of the order of magnitude of α=100-200 mu.m in this case. The matrix has a conical through-passage which communicates with the conical surface of the locking screw. The locking screw rigidly draws the cap-shaped matrix fast in place for fixedly locking the mounting cap. In eccentric oblique loading, this corresponds to a maximum angular displacement “α” of 1°-2°, which is considered as fully satisfactory in view of possible connection to natural teeth.
The connecting device further includes a sleeve-shaped patrix, for example of titanium, plastic or gold, fitted with a heel which depresses the O-ring, and a inner portion running at right angles to the heel and enclosing, together with the heel, the matrix abutment or shelf and the matrix wall, the O-ring in a round tunnel of rectangular cross-section. In the production of the crown or bridge construction, respectively, the patrix is cast or fixed by other means in the crown/bridge which, through this patrix, will be elastically anchored to the matrix—the locking screw—the spacer. The resilient anchorage is locked by means of the ring nut, also manufactured of, for example, gold. The ring nut is threaded down to a light pre-tensioning of the O-ring, marked by a groove in the upper edge of the nut which must then register with a corresponding groove marking in the upper edge of the matrix. By a further two such markings in the matrix edge, both moderate and hard pre-tensioning of the connecting device are permitted. The upper surface of the connecting device may be covered with, for example, a gold washer, once the nut and the locking screw have been locked by a droplet of acrylate. Acrylate is applied over the gold washer in order to fill the aperture in the crown/bridge construction through which the locking screw and the ring nut have been sited in place.
This device is complex and requires a high-quality rubber O-ring, precision metals (e.g. such as a gold) and the patrix has to be elastically anchored to the matrix-the locking screw-the spacer, that is extremely expensive.
The aim of the present invention is therefore to provide a dental implant which does not have the mentioned above various disadvantages.
Thus, there is a great need in the art for the improved not complex, not expensive and reliable universal dental implant embedded in the bone of a person's (a dental patient's) jaw with the connecting portion for the crowns.